Cancer is the first-ranked disease among causes of death in Japan, and its therapies are in need of improvement. In particular, lung cancer is at the top of the causes of cancer death not only in Japan but also throughout the world, causing over a million deaths each year. Lung cancer is broadly divided into small-cell lung carcinoma and non-small-cell lung carcinoma, and the non-small-cell lung carcinoma is subdivided into three subgroups: lung adenocarcinoma (LADC), lung squamous cell carcinoma, and large-cell carcinoma. Among these subgroups, LADC accounts for about 50% of all cases of non-small-cell lung carcinoma, and besides its frequency is elevated (Non-patent Document 1).
It has been found that a considerable proportion of LADCs develop through activation of oncogenes. It has also been revealed that when the activation of oncogenes occurs, somatic mutations in the EGFR gene (10-40%) or the KRAS gene (10-20%), fusion between the ALK gene and the EML4 (echinoderm microtubule-associated protein-like 4) gene, fusion between the ALK gene and the KIF5B gene (5%), or other alterations occur in a mutually exclusive way (Non-patent Documents 2-6).
In the field of human cancers including lung adenocarcinoma, there is a strong need for identifying oncogenes involved in the onsets of such cancers, such as mutant genes (mutant proteins) and fusion genes (fusion proteins), because such an identification will greatly contribute to development of novel cancer treatment and testing methods targeting such genes.
In particular, advanced lung cancers are mainly treated with drugs, but individual patients exhibit greatly different responses to a drug, so there is needed a means for predicting what drug is therapeutically effective in each case. Thus, identification of molecules that can serve as indicators for such predictions, such as mutant genes and fusion genes is in progress, as noted above; for example, it has been shown that tyrosine kinase inhibitors targeting EGFR and ALK proteins are particularly effective for treatment of LADCs harboring EGFR mutations and/or ALK fusions. Further, a technique for detecting a fusion of the ALK tyrosine kinase gene as observed in 4-5% of lung cancer cases has been developed as a method to screen for cases to be indicated for an inhibitor against ALK protein tyrosine kinase, and its clinical trials are currently underway.
However, a thorough elucidation of fusion genes and the like in various cancers including lung cancers has not yet been achieved, and there is still a demand for identifying mutant genes and fusion genes that can serve as indicators for predicting the effectiveness of drug treatments.